This German Article, published by Trautonium virtuoso Oscar Sala in the "Zeitschrift für Schwingungs- und Schwachstromtechnik" in December 1943 does not only describe the Trautonium's principle of operation. There is a lot of theoretical discussion about sound generation, wave shaping and linearity. This might be of interest for theremin builders.
Up to now an English translation does not (yet) exist. Please contact Thierry with specific questions.